Control instruments for kilns or ovens



Jung 25, 1957 c. H. STRANGE conmoumsmmms FOR xmzs on owns Filed Oct. 5, 1955 ATTORNEY INVENTOR. 6 CHARLES HETRANGE 41 BY 13?;

soc Anis \2 CGNTROL INSTRUMENTS FGR KlLNS R OVENS Charles H. Strange, Jacksonville Beam, Fla.

Applicationfictoher 5, 1955, Serial No. 538,741

21 Claims. ((31. 200-137) This invention relates to heat control instruments for kilns or ovens wherein a thermo-expansive element opcrates a micro switch in a manner somewhat as described in my Patent No. 2,705,746. of April 5, 1955.

l have found that I may employ an expansive member whose dimensions change relative to kiln, dimensions with a high degree of accuracy even though the kiln itself undergoes a considerable change in size and so avoid the use of ceramic expansion elements, which are liable to breakage, and are undesirably heavy if large enough to be strong.

An object of the invention is to provide a kiln control in which only one expansive element is used. and which need not support anything more than its own weight.

Another object is to provide such an expansive element that, will be exposed to the interior of the kiln.

Another object is to provide a heat control. compensator for an expansive element passing through the kiln to correct for change in kiln dimensions.

These and other objects, that will be apparent from a reading of the description, are attained in a combination which, briefly described, includes a, kiln with an expansive element passing through the kiln. One, end of the element remains in an approximately fixed position Figure 2 is a vertical sectional view of the kiln with details of construction.

Figure 3 is a sectional view showing the compensating means, the section being taken substantially along the line 3 .3 of Figure 2 looking in the direction of the arrowsof said line.

Figure 4 shows the face of a dial plate.

Figure 5 shows the expansive element in. only one; wall of therkiln.

Figure 6-shows the compensating means in a dilferent form and Figure 7 show details of a means for rotating the expansivev element.

The invention. is shown in connection with an. oven or kiln. 10 having opposed: refractory walls 11a, 11b and rear Wall 110 and an exterior casing 12. The term wall is used however in a generic sense and may include a.

top andbottom being as the position. of the kiln does not generally affect the operation of the invention.

The temperature of thekiln is regulated bya thermostat, generally designated 14, which includes a. long ex- A par s, ar c rried tates Patent rid pansion rod 15 passing through the kiln, either through alined bores or holes 16, 18 in opposed walls 11a and 11b or through a continuous bore or hole 17 in one of the walls generally designated 11 in Figure 5. Thus the rod may be exposed to gases within the kiln or at least partially isolated from them depending on the location. The thermostat is more sensitive to temperature changes if the rod is disposed as in Figure 2 rather than as in Figure 5, since the rod is rapidly heated or cooled by radiation and convection. However, if the rod is exposed it may be subjected to extremely high temperatures and economically available metals, normally used for expansion elements, cannot stand temperatures above about 2,400F. For temperatures not exceeding this temperature and where the rod is to be exposed, the rod may be of such material as Inconel or Kanthall described in my United States Patent No. 2,705,746. At lower temperatures, other known suitable metals may be used.

If great sensitivity is not needed, but high temperatures are, the rod is disposed in a wall and not exposed to the interior of the kiln. The expansion of the rod is therefore governed by the temperature of a section, of the wall rather than that of the interior of the kiln. Often, however, a slight temperature drop through a small thickness of wall may enable the use of a metal expansion member that would be useless if it were exposed to melting temperatures within the kiln. Some degree of control is better than none, and the same instrument can be used, Whether the temperature measured is that of the interior wall surface or of a section between outer and inner surfaces, with appropriate calibration.

As. shown in Figure 2 one end portion; 1-9 of the rod.

15 is provided with, threads 20- engaged in a threaded member or nut 21 mounted fast with respect to a portion 12a. of the casing 12 adjacent the outer wall surface 22a of wall 11a.

rotated by a knob- 26 sothat the threads cause the rod to move in the direction of its axis, so that, at a given temperature the other end 28 of the; rod. maybe made to move toward or away from the button 29- of a microswitch 30 mounted on the casing portion 12b adjacent the wall 11b at the outer surface thereof 22b.

Since the thermostat operates by a longitudinal expansion or contraction of the rod 15 and for a given setting the dial end- 20 of the rod is fixed relative to the kiln. case, the switch 30 should not be; mounted directly onto.

cause the; sheet 32: to, move and. carry the micro switch thereon toward the rod..

The plate 32 is secured at opposite marginal portions 34', as by screws. 35, to the casing portion 12b and spaced therefrom as the marginal portions by spacers 36. The

plate 32 is slightly bowed with its mid portion projecting toward the kiln and: provided with a more or less central hole 38 through which the rod end 23 passes.

As the plate is heated by the kiln it becomes longeror more bowed and so brings the intermarginal portion, on which the switch is mounted, closer to the rod end 28.

A tie plate 39 of material such as steel having'alower j coefiicient of expansion than that of the bow plate 32, between it and the switch, and secured at opposite marginal'portions 40 to marginal portions 34 prevents spreading of screws 35 as the plate 32 expands. The-tie plate is. provided with a holedl coaxial" with hole 38; topass The nut is fast on a dial plate 24 which. is. secured to portion 12a as by screws, 25. The rod is.

the rod and with holes 42 to pass the mounting screws. The hole 41 may serve as a bearing for the rod.

The bores 16, 17 and 18 may contain talc as a lubricant for the rod and to minimize diffusion of gases through the walls. The dial plate 24 may be provided with temperature indicia 44.

Compensation for kiln-size change by movement of the switch 30 is preferable but a similar effect may be obtained from movement of the entire rod in relation to the exterior temperature of the kiln as shown in Figure 6 wherein the switch is mounted fast on the case and the same bow plate 32 secured to the case in the manner previously described of Figure 2. In Figure 6, however, the nut 21 is fast on the bow plate and the holes 42 are omitted from the tie plate 39, but the rod may pass through the hole 41 to carry the knob 26. In this construction the tie plate bears the indicia. If the construction of Figure 6 is to be used by careless operators who may force the bow plate 32 it is desirable to prevent direct application of manual force to the rod and employ a coupling to permit only torque to be transmitted from the knob 26 to the rod. Such a coupling is shown by way of example in Figure 7 wherein a double collared stub shaft 45 mounted on the tie plate 39 bears the knob and is provided with a diametric end slot 46 receiving a flat tongue on the end 19 of the rod.

In operation, as the rod expands due to heat in the kiln the rod engages the button 29 and actuates the switch to reduce the heat by known means. As the kiln walls heat up they become longer and wider which tends to cause the switch to recede from the rod end. Heat picked up from the walls by the bow plate causes the latter to become more bowed toward the wall and brings the switch with it to compensate for kiln expansion.

In general, the kiln walls are usually of ceramic material, as shown in the drawing, which has a very low coeificient of thermal expansion. However, the casing 12 is usually of material having a much higher coefiicient so that when a cold kiln is heated there is little change in kiln size until the casing becomes heated. Due to the relatively slow conduction of heat through the ceramic material, changes in casing dimensions and changes of temperature in the kiln may lag one another by a considerable period of time.

I claim as my invention:

1. In combination, a kiln having a wall and a bore therein; a thermo-expansive rod in the bore and passing through the kiln; a switch mounted on the exterior of the kiln having an operative part adjacent one end of the rod for engagement therewith; and means for mounting the other end portion of the rod, and means for maintaining said other end portion a predetermined distance from said part during changes of the dimensions of kiln with temperature.

2. In combination, a kiln having a wall with a bore in 4 the wall; a thermo-expansive longitudinal member in the bore and passing through the kiln; a switch carried on the kiln and having an operative part disposed adjacent one end portion of the member for engagement therewith; a part carried on the kiln for mounting the other end portion of the member, and means for maintaining the said parts a substantially constant distance apart when the kiln changes size with variations of temperature.

3. In a combination as claimed in claim 2, said means being an expansion member fast with respect to the switch and carried on the kiln.

4. In a combination as claimed in claim 2, said means being an expansion member fast with respect to the second mentioned part and carried on the kiln.

5. In a combination as claimed in claim 2, the member being exposed to the interior of the kiln.

6. In combination, a kiln having a wall with a bore in the wall; a thermo expansive rod in the bore and passing through the kiln; a thermo expansive plate having opposite marginal portions secured to and fast with respect to the exterior of the kiln and spaced therefrom, the plate being bowed toward the kiln between said portions, the rod passing through the plate; a switch having a button and case member; a threaded member; one of said members being mounted fast on said plate between said portions, the other member being mounted on the kiln, the rod passing through the threaded members at one end portion and having the other end portion adjacent the button for engagement therewith.

7. A combination as claimed in claim 6, said other member being fixed and fast on the kiln.

8. In combination, a kiln having a wall with a bore in the wall; a thermo-expansive rod in the bore and passing completely through the kiln; a thermo-expansive plate having opposite marginal portions secured on and fast with respect to the exterior of the kiln and spaced therefrom, the plate being bowed toward the kiln between said portions; a tie piece to prevent further separation of the portions when the plate expands; the rod passing through the plate and piece; a switch having a button and mounted fast on said plate between said portions, a nut mounted on the kiln, the rod passing through the nut and threaded at one end portion and having the other end portion adjacent the button for engagement therewith.

9. In a combination as claimed in claim 8 and means for rotating the rod.

10. In combination, a kiln having a wall with a bore in the wall; a thermo-expansive rod in the bore and passing through the kiln; a thermo-expansive plate having opposite marginal portions secured on and fast with respect to the exterior of the kiln and spaced therefrom, the plate being bowed toward the kiln between said portions; a switch having a button; a nut; said nut being mounted fast on said plate between said portions, the switch being mounted fast on the kiln, the rod passing through the nut and plate at one end portion and having the other end portion adjacent the button for engagement therewith; a tie plate having marginal portions secured to the expansive plate marginal portions; a stub shaft mounted on the tie plate and alined with the rod, and coupling means between the shaft and rod permitting axially longitudinal motion therebetween.

11. In combination, a kiln having walls, two being opposed walls, one wall having a bore therein, a thermoexpansive rod in the bore and passing through the kiln; a thermo-expansive plate having opposite marginal portions secured to and fast with respect to the exterior of one wall of the kiln and spaced therefrom, the plate being bowed toward the kiln between said portions, the rod passing through the plate; a switch having a button and switch member; a threaded member; one of said members being mounted fast on said plate between said portions, the other member being mounted fast on the exterior of the opposite wall of the kiln, the rod passing through the threaded member at one end portion and having the other end portion adjacent the button for engagement therewith.

12. In combination, a kiln having walls, two being opposed walls, one wall having a bore therein, a thermoexpansive rod in the bore and passing through the kiln; a thermo-expansive plate having opposite marginal portions secured to and fast with respect to the exterior of one wall of the kiln and spaced therefrom, the plate being bowed toward the kiln between said portions, the rod passing through the plate; a switch having a button and switch member; a threaded member; one of said members being mounted fast on said plate between said portions, the other member being mounted fast on the exterior of the opposite wall of the kiln, the rod passing through the threaded member at one end portion and having the other end portion adjacent the button for engagement therewith; and a tie plate spanning the expansive plate and secured thereto at the marginal portion and provided with a hole alined with the rod. 7 r

13. In combination, a kiln having walls, two being opposed walls, one wall having a bore therein, a thermoexpansive rod in the bore and passing through the kiln; a thermo-expansive plate having opposite marginal portions secured to and fast with respect to the exterior of one wall of the kiln and spaced therefrom, the plate being bowed toward the kiln between said portions, the rod passing through the plate; a switch having a button and switch member; a threaded member; one of said members being mounted fast on said plate between said portions, the other member being mounted fast on the exterior of the opposite wall of the kiln, the rod passing through the threaded member at one end portion and having the other end portion adjacent the button for engagement therewith; and a tie plate spanning the expansive plate and secured thereto at the marginal portion and provided with a hole alined with the rod; and bolts passing through the tie plate.

14. In combination, a chamber structure having a wall and subject to size changes with temperature; a longitudinal expansion element passing through the structure and movable with respect thereto; a sensing member carried on the exterior of the chamber structure and adjacent one end portion of the element; a support member for the other end portion of the element and adjustable to a selected fixed position along the axis of the element, the support member being carried on the structure exterior thereof, and compensating means responsive to the structure temperature for maintaining a predetermined distance between the two members to eliminate the effect of structure expansion with temperature.

15. A combination as claimed in claim 14, said means being a second expansion member adjacent the exterior of the structure and having a part secured with respect thereto and another part secured to one of said members for imparting compensatory movement thereto, the second expansion member being substantially completely exterior of the structure to minimize response by the second expansion member to changes of temperature within the chamber.

16. A combination as claimed in claim 15, said one of said members being a nut in threaded engagement within the element and serving as said support member.

17. A combination as claimed in claim said one of said members being a switch and serving as said sensing member.

18. In combination, a kiln and case therefor; a rod of expansive material passing through the kiln; an expansive bowed plate and a plate bearing indicia each having marginal portions fast on the case of the kiln and spaced therefrom, the bowed plate having its medial portion bowed toward the kiln; a switch exterior of the kiln and having an operative part alined with said rod and adjacent thereto at one end portion thereof for engagement with the rod as the latter expands; said how plate being provided with an opening through which the rod passes; the other end portion of the rod being provided with threads; a nut on said threads and fast on one of the plates, and knob and pointer means axially alined with the rod for rotating same and moving the rod toward and away from said part and associated with the indicia.

19. In combination, a kiln and an expansion rotary rod passing therethrough, a sensing device carried on the exterior of the kiln and adjacent one end portion of the rod for responding to longitudinal displacement of said end portion as the rod expands; the other end portion of the rod being provided with threads; a nut member carried on the kiln and disposed on the rod and engaging the threads, and substantially non-rotary with respect to the kiln and the axis of the rod, so that rotation of the rod will alter the position of said one end portion relative to said nut member in the direction of said axis for temperature settings, and compensating means for keeping the nut a predetermined distance from the sensing device during changes of kiln dimensions with temperature changes of the kiln.

20. In a combination as claimed in claim 19, and knob means for rotating the rod and connected to said other end portion.

21. In a combination as claimed in claim 20 and means for permitting longitudinal movement of the rod with respect to said knob means when the rod and knob means are rotated together.

References Cited in the file of this patent UNITED STATES PATENTS 1,225,648 Kleckner May 7, 1917 1,829,416 Lobley Oct. 27, 1931 2,151,319 Finch Mar. 21, 1939 2,210,526 Burling Aug. 6, 1940 

